Reverse flow gas turbine engine airflow bypass

ABSTRACT

A gas turbine engine has a propulsor including a fan and a power turbine, an engine core aerodynamically connected to the propulsor by a transition duct, and a bypass valve in the transition duct that allows for air from the engine core to bypass the power turbine.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority from U.S. Provisional Application No.61/773,908, filed Mar. 7, 2013, for “REVERSE FLOW GAS TURBINE ENGINEAIRFLOW BYPASS”.

BACKGROUND

This application relates generally to a gas turbine engine for anaircraft, and more specifically, to a reverse flow gas turbine enginethat contains an airflow bypass.

Jets and aircraft powered by gas turbine engines typically have smallauxiliary engines at the back end, often referred to as auxiliary powerunits (APUs). These engines often have no fan, and are considered lowpressure ratio devices. The APU provides ground power to operate cabinsystems, such as the environmental control system (including airconditioning) and powering the electronics of the aircraft cabin, aswell as provide start-up potential for the flight engines. APUscurrently are parasitic hardware, i.e., the unit is used on the ground,but it is seldom used in flight. Thus, most APUs are considered wasteweight on an aircraft. Typical APUs may generate enough ground power,but flight engine cores are also actuated often on the ground. APUstypically turn off automatically when flight engine cores are activated.

With the cores getting smaller in large pressure ratio geared turbofanengines, the core size for a single isle jet or aircraft is similar tothe prior art APU. Elimination of the APU from an aircraft is desired tosave weight, and thus fuel burn which is in direct proportion to theweight of a jet or aircraft.

SUMMARY

In one embodiment, a gas turbine engine has a propulsor including a fanand a power turbine, an engine core aerodynamically connected to thepropulsor by a transition duct, and a bypass valve in the transitionduct that allows air from the engine core to bypass the power turbine.

In another embodiment, an aircraft has an aircraft body and an engineattached to the aircraft body. The engine includes a propulsor having afan and a power turbine, an engine core aerodynamically connected to thepropulsor by a transition duct, and an airflow bypass in the transitionduct that allows for the airflow from the engine core to bypass thepower turbine.

In yet another embodiment, a gas turbine engine has a propulsor, a gasgenerator aerodynamically connected to the propulsor by a transitionduct, and an airflow bypass in the transition duct that allows for theventing of airflow from the engine core to bypass the propulsor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a reverse core engine.

FIG. 2 is a cross sectional view of an engine mounted to an aircraftwing.

DETAILED DESCRIPTION

The present application relates to reverse core gas turbine engines. Thereverse core engine contains a bypass valve in the transition ductbetween the propulsor and engine core. The valve may be activated duringground operation to bypass the power turbine and allow the engine tooperate without using the power turbine and propulsion fan.

FIG. 1 is a schematic view of a reverse core engine. Engine 10 includesa propulsor 12 at a forward end which is centered for rotation about anaxis X. Propulsor 12 includes a fan 14 and a nozzle 16 rearward thereofsurrounded by a nacelle 18. Axis X is also a central axis of the fan andthe nozzle. Engine 10 may include a gear reduction 20 driven by a powerturbine section 22 to drive the fan 14.

A core engine 24 includes combustion section 26 positioned between aturbine section 28 and a compressor section 30. The core engine 24 mayalso be referred to as the gas generator of the turbine engine. Air fromnacelle 18 passes into an inlet duct 32 to be delivered to thecompressor 30. The duct 32 is over a limited circumferential extentwithin nacelle 18. At other circumferential locations within nacelle 18,air flows as bypass air for propulsion. The air is compressed anddelivered into combustion section 26, where it mixes with fuel and isignited. Products of this combustion pass through turbine section 28,which drives compressor section 30. The products of combustion then passthrough a transition duct 34 over power turbine section 22, to drive thefan 14 that is connected by thereto by a propulsor shaft 36. Air thenexits the power turbine 22 and is exhausted therefrom, such as by havinga nozzle that directs the flow aftward upon leaving the power turbine22.

The illustrated gas turbine engine is a “reverse flow engine” in thatthe compressor 30 is positioned further into (forward to aft) the enginethan is the turbine 28. That is, the turbine section 28 is closest tothe propulsor 12, the combustor section 26 and the compressor section 30are positioned further away in the downstream or aft direction of thepropulsor 12 relative to the turbine section 28.

The engine 10 is positioned such that the fan 12, the gear 20, and thepower turbine 22 are positioned centered on the axis X, while the coreengine 24, including the compressor section 30, the combustor section26, and the turbine section 28, is positioned on a non-parallel axis Y.The core engine 24 may be mounted in some manner to the nozzle 16, suchas through transition duct 34.

In an engine that is reverse flow, and in particular in one wherein theaxes X and Y are not parallel, a relatively long core engine 24 can beachieved without the core engine blocking the exit area 38. However, theoverall length of the engine 10 is reduced as the core engine 24 ismounted at an angle with respect to the propulsor 12.

FIG. 2 is a cross sectional view of the engine 10 mounted to an aircraftwing 40. Many of the same elements as shown in FIG. 1 are alsoillustrated in FIG. 2: the engine 10 with the propulsor 12 having thefan 14 and the nozzle 16 surrounded by the nacelle 18, and the coreengine 24 with the combustor section 26, the turbine section 28, and thecompressor section 30 aligned along core engine shaft 42. The inlet duct32 extends from the propulsor 12 to the compressor section 30 of thecore engine 24. The transition duct 34 aerodynamically connects theturbine section 28 of the core engine 24 with the power turbine 22.

During normal operation, gases and airflow leaving the turbine section28 will flow through the transition duct 34 into the power turbine 22,which will turn the propulsor shaft 36. The gear reduction 20 willchange the speed of the propulsor shaft 36 as delivered to the fan 14 sothat the fan 14 will run at a different speed than that of the powerturbine 22. Typically, the gears are sized to slow the speed of the fan14.

The transition duct 34 may contain a flow bypass 44. The flow bypass 44will allow pressurized air from the turbine section 28 to leave thetransition duct 34 prior to the power turbine 22. That is, the flowbypass 44 disrupts the aerodynamic connection between the turbinesection 28 of the core engine 24 with the power turbine 22 of thepropulsor 12. Thus, the fan 14 will not run when the flow bypass 44 isopen to allow venting of the airflow.

In one embodiment, the flow bypass 44 is a valve, such as a butterflyvalve. The valve is controlled from the cockpit of the aircraft. In oneembodiment, the valve may be designed so that any forward motion of theaircraft will automatically trigger the close of the flow bypass 44.When opened, the pressurized air will flow through the flow bypass 44 asthe path of least resistance, and thus not drive the power turbine 22.Although disclosed as a single valve, it is envisioned that multiplevalve may be circumferentially placed about the transition duct 34.Similarly, any type of controllable valve may be used, including but notlimited to ball, gate, globe, pin, angled or straight flow, and thelike.

Hardware 46 may be attached to the core engine 24. The hardware willprovide the functions that are typical of an auxiliary power unit (APU),such as providing airflow for the environmental control system, andgenerating power for the aircraft electronics. The system describedeliminates the need for a separate APU on the aircraft. This results ingreat weight savings, and thus produces a more efficient aircraft as theweight of an aircraft is directly proportional to the fuel burn of anengine. Also, the system is more efficient due to the high pressureratio of the core engine due to its design for flight.

The flow bypass 44 may be activated during ground operation to bypassthe power turbine 22 and allow the engine 10 to operate without usingthe power turbine 22 and the propulsor 12. Thus, the engine 10 mayoperate as an APU during ground operation. This removes the requirementfor an additional, separate engine to act as the APU on the aircraft.

Discussion of Possible Embodiments

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

A gas turbine engine has a propulsor including a fan and a powerturbine, an engine core aerodynamically connected to the propulsor by atransition duct; and a bypass valve in the transition duct that allowsfor air from the engine core to bypass the power turbine.

The gas turbine engine of the preceding paragraph can optionallyinclude, additionally and/or alternatively, any one or more of thefollowing features, configurations and/or additional components:

the engine core includes a compressor section, a combustor section, anda turbine section, with the turbine section being closer to thepropulsor than the compressor section;

the propulsor delivers air into the compressor section through a flowinlet duct;

the engine core is attached to the transition duct and flow inlet duct;

the propulsor has a first axis and the engine core has a second axis;

the first axis and second axis are not parallel;

the power turbine is positioned downstream of the turbine section of theengine core; and further comprising a gear reduction between the powerturbine and the fan of the propulsor to cause the fan to rotate at aslower speed than the power turbine;

the power turbine rotates on the first axis; and/or

the bypass valve is a butterfly valve.

In another embodiment, an aircraft has an aircraft body and an engineattached to the aircraft body. The engine includes a propulsor having afan and a power turbine, an engine core aerodynamically connected to thepropulsor by a transition duct, and an airflow bypass in the transitionduct that allows airflow from the engine core to bypass the powerturbine.

The aircraft of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

the engine core includes a compressor section, a combustor section, anda turbine section, with the turbine section being closer to thepropulsor than the compressor section;

the propulsor delivers air into the compressor section through a flowinlet duct;

the engine core is attached to the transition duct and flow inlet duct;

the propulsor has a first axis and the engine core has a second axis;

the first axis and second axis are not parallel;

the power turbine is positioned downstream of the turbine section of theengine core; and further comprising a gear reduction between the powerturbine and the fan of the propulsor to cause the fan to rotate at aslower speed than the power turbine;

the power turbine rotates on the first axis;

the airflow bypass is a valve; and/or

the valve is a butterfly valve.

In yet another embodiment, a gas turbine engine has a propulsor, a gasgenerator aerodynamically connected to the propulsor by a transitionduct, and an airflow bypass in the transition duct that allows for theventing of airflow from the engine core to bypass the propulsor.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A gas turbine engine comprising: a propulsor including a fan and apower turbine; an engine core aerodynamically connected to the propulsorby a transition duct; and a bypass valve in the transition duct thatallows for air from the engine core to bypass the power turbine.
 2. Thegas turbine engine of claim 1, wherein the engine core includes acompressor section, a combustor section, and a turbine section, with theturbine section being closer to the propulsor than the compressorsection.
 3. The gas turbine engine of claim 2, wherein the propulsordelivers air into the compressor section through a flow inlet duct. 4.The gas turbine engine of claim 3, wherein the engine core is attachedto the transition duct and flow inlet duct.
 5. The gas turbine engine ofclaim 1, wherein the propulsor has a first axis and the engine core hasa second axis.
 6. The gas turbine engine of claim 5, wherein the firstaxis and second axis are not parallel.
 7. The gas turbine engine ofclaim 6, wherein the power turbine is positioned downstream of theturbine section of the engine core; and further comprising: a gearreduction between the power turbine and the fan of the propulsor tocause the fan to rotate at a slower speed than the power turbine.
 8. Thegas turbine engine of claim 7, wherein the power turbine rotates on thefirst axis.
 9. The gas turbine engine of claim 1, wherein the bypassvalve is a butterfly valve.
 10. An aircraft comprising: an aircraftbody; an engine attached to the aircraft body including: a propulsorhaving a fan and a power turbine; an engine core aerodynamicallyconnected to the propulsor by a transition duct; and an airflow bypassin the transition duct that allows for airflow from the engine core tobypass the power turbine.
 11. The aircraft of claim 10, wherein theengine core includes a compressor section, a combustor section, and aturbine section, with the turbine section being closer to the propulsorthan the compressor section.
 12. The aircraft of claim 11, wherein thepropulsor delivers air into the compressor section through a flow inletduct.
 13. The aircraft of claim 12, wherein the engine core is attachedto the transition duct and flow inlet duct.
 14. The aircraft of claim10, wherein the propulsor has a first axis and the engine core has asecond axis.
 15. The aircraft of claim 14, wherein the first axis andsecond axis are not parallel.
 16. The aircraft of claim 15, wherein thepower turbine is positioned downstream of the turbine section of theengine core; and further comprising: a gear reduction between the powerturbine and the fan of the propulsor to cause the fan to rotate at aslower speed than the power turbine.
 17. The aircraft of claim 16,wherein the power turbine rotates on the first axis.
 18. The aircraft ofclaim 10, wherein the airflow bypass is a valve.
 19. The aircraft ofclaim 18 wherein the valve is a butterfly valve.
 20. A gas turbineengine comprising: a propulsor; a gas generator aerodynamicallyconnected to the propulsor by a transition duct; and an airflow bypassin the transition duct that allows for the venting of airflow from theengine core to bypass the propulsor.